Add equality operator
Add comparison operators and interface comments
- By defining less-than, all other comparisons are now defined.
  Less than checks first if the number of digits of the two are equal.
    If not, the one with more digits is greater.
  If so, it goes through each digit, from most significant to least.
    For each, if the digits are not equal, then the one with the greater
    digit is greater.  Further comparisons are only needed if all more-
    significant digits were equal.